1. Field of the Invention
This invention relates to a numerical control unit having a cassette type memory, and more particularly to a numerical control unit having a cassette type semiconductor memory which is constructed to be detachably mounted on the numerical control unit.
2. Description of the Prior Art
In the prior art, a numerical control unit operates while reading out command data from a paper tape. There have recently been increased apparatus of the type that a memory for storing command data is built into the numerical control unit.
The reasons for this are as follows:
(1) Since no paper tape is used, reliability is high in the case of repeating a machine work.
(2) At the machining site, the operator can directly store command data in the memory to perform machining.
(3) At the machining site, the command data can readily be corrected.
(4) With the progress of semiconductor techniques, it has become possible to use a high-density and inexpensive memory.
By the way, in such a numerical control system, the internal memory for storing the abovesaid command data has recently been demanded to fill the following needs:
(1) The kinds of articles to be worked and the frequency of change and the amount of command data differ with customers and the capacity of the memory required therefor differs with the model. Therefore, it is desired that the capacity of the command data memory of the numerical control unit be easily increased or altered in response to the customer's request.
(2) There are some occasions when one wishes to utilize the command data corrected and stored in the memory of one numerical control unit with other additional numerical control units of the same kind.
If the requirement (1) is satisfied, the cost of the apparatus can be reduced and if the requirement (2) is fulfilled, the working efficiency can be remarkedly enhanced.
However, for satisfying the requirement (1), it is necessary to increase the capacity of the memory in advance, so that when the amount of command data is small, it is uneconomical. Further, for fulfilling the requirement (2), it is necessary to interconnect the numerical control units so that data transmission can be effected, and this is difficult to realize.